Experiments are normally conducted with a typical linear flow rate of 25 cm/d, which corresponds to the rate of the injected flow front in the reservoir.

The most frequently used testing method utilizes pulse injection into the core. The tracer candidate is always co-injected with a standard reference tracer. For water, this is normally HTO. The production profiles of the tracer candidate and the standard reference tracer may be directly compared. Examples of such profiles are given in Fig. 3. Figure 4 shows the difference curve of the normalized production profiles.

Another method that may be used is continuous injection of a constant concentration tracer solution. Figure 43 show results from such a test at ambient temperature where In3+ complexed with EDTA is compared with the behaviour of HTO. The curves show evidence of a slight reversible sorption of In-EDTA under the running conditions.

When a tracer candidate has also passed the dynamic tests in ‘good shape’, the next, and final, step is to perform a pilot test in an actual reservoir section. An

1. Electric heating elements

2. Thermally insulated column housing

3. Thermo elements

4. Air circulation pump

5. Balance

6. Column elution liquid

7. High-pressure pump

8. Piston cylinder

9. Six-port valve

10. Constant initial trac er mixture volume

11. Syringe for filing of tracer volume

12. Computer for logging

13. Differential pressure gauge

14. Collected liquid samples

15. Circulating ho t air

16. Pressure equalizer

17. Back-pressure regulator

18. Sample changer

19. Nitrogen reservoir for dome pressure

20. Chromatographic column with crushed reservoir material

FIG 42. Flow rig for dynamic tracer testing of water tracers in columns of crushed reservoir rock or reservoir-like material under simulated reservoir conditions. The rig contains a 200 cm long thermostatized chromatographic column.

acceptable tracer performance may finally be regarded as proven after several successful experiments under reservoir conditions.